In the CDMA portable telephone system in, for instance, a UMTS (Universal Mobile Telecommunication System) or the like, a simultaneous transmission and reception can be carried out by using a plurality of different frequency bands and the frequency bands can be switched respectively for the transmission and the reception to perform a communication.
In a radio communication device used in such a radio communication system, a band switching signal common to a transmitting part and a receiving part is generated in a base band signal processing part or a control part. Th band switching signal has been ordinarily used to switch the frequency bands respectively for the transmitting part and the receiving part. Further, in a compressed mode upon switching the frequency bands, an exclusive switching signal and timing for switching the frequency bands have usually needed to be set and prepared.
As an example of the radio communication device capable of transmitting and receiving in a plurality of frequency bands, a device has been known which includes a voltage control oscillator that has a plurality of oscillating stages for oscillating one or more frequency bands and selectively switches and operates the oscillating stages and a local oscillator having a variable frequency divider with a variable frequency dividing ratio for dividing a part of the output of the voltage control oscillator to supply the frequency divided output to a phase comparator. The oscillating stages of the voltage control oscillator have been switched to oscillating stages respectively corresponding to a plurality of mobile telecommunication systems using different radio frequency bands to oscillate. According to this structure, local oscillating frequencies to the plurality of mobile telecommunication systems can be supplied by the local oscillator composed of one PLL frequency synthesizer (for instance, see Patent Document 1).
Further, to meet a multi-mode radio communication, there is a multi-mode radio communication converter including a transmit and receive mixer part having an antenna of a plurality of or multiple bands capable of being selected and an oscillator capable of being oscillated by a plurality of oscillating frequencies that can be selected to convert the frequency of a first input signal by using one oscillating frequency selected from the plurality of oscillating frequencies, a modulating/demodulating part for modulating/demodulating a second input signal so as to meet one communication system selected from a plurality of communication systems and a specific modulating/demodulating part for modulating/demodulating a third input signal so as to meet a specific radio communication system. Such a converter is employed so tat an existing communication terminal can be used in a different radio communication system as it is (for instance, see Patent Document 2).
(Patent Document 1) JP-A-2000-244360
(Patent Document 2) JP-A-2000-269848
However, in the above-described usual radio communication device, the common frequency band switching signal is supplied to the transmitting part and the receiving part to switch the frequency band. Accordingly, for instance, when only the receiving part is switched to another frequency band, the state of a communication line (a downward line) from a base station to the radio communication device is hardly monitored without disconnecting a communication line (an upward line) from the radio communication device to the base station, or an actual communication hardly performed.
Further, in a usual frequency band switching method, the frequency band switching signal is generated in the base band signal processing part or the control part. Thus, when independent band switching signals are desired to be obtained respectively in the transmitting part and the receiving part, hardware needs to be added to the base band signal processing part or the control part. Therefore, a circuit scale is increased and the number of interface signal lines is increased so that the structure of the device is undesirably enlarged and complicated.
Further, in a system having a time offset in the boundary of time slots of the transmission and the reception of the simultaneous transmitting and receiving system, an individual antenna is prepared for each frequency band. In this case, even when separate band switching signals are prepared separately for transmitting and receiving, it is not suitable to commonly use the band switching signals as antenna switching signals upon compressed mode operation. Therefore, exclusive band switching signals for switching the antennas are separately required.
The present invention is proposed to solve the above-described problems and it is an object of the present invention to provide a radio communication device in which frequency bands can be individually switched respectively in a transmission and a reception with a simple structure without making the structure of the device enlarged or complicated, only a receiving part can be switched to another frequency band without disconnecting an upward line during a communication or the state of a downward line in another frequency band can be monitored or a communication can be performed.